Agglutinins, as substances with antibody-like properties, play an important role in the immune response. We will determine the agglutinating activity of earthworm coelomic fluid against bacteria and vertebrate erythrocytes, the specificity of binding, and the physical and chemical characteristics of agglutinins. Another aspect will be to determine which of the coelomocyte(s) is responsible for synthesizing the agglutinin. Finally, some attention will be devoted to defining the biologic function of agglutinins. For the first time, the aims of this proposal promise to elucidate what may emerge as the identification of the recognition unit or receptor in an invertebrate. Defining the receptor would do much to piece together fragmented information concerning the origins of immunologic recognition and specificity. Associating the receptor with a particular cell would tell us where in the phylogenetic scale immunologic receptor cells first appeared. Both of these phenomena, the receptor and the cell in which it is synthesized, would add greatly to our understanding of how the immune sytem of more complex vertebrates evolved.